1. Field of the Invention
This invention relates to a method for reducing ore; and more particularly to an improved FIOR method for producing a stable, reduced iron ore from ore fines.
2. Description of the Prior Art
Previously, there have been a number of methods and processes for reducing ore by means of fluidized-bed reactors, which use gas or gas mixtures to reduce the ore and to fluidize the bed. The reducing and fluidizing gas for these processes is produced in special plants, for instance by the steam-reforming process, starting from hydrocarbons and steam. However, that process requires separate plants for gas production and these are very costly, thus markedly increasing the cost of the final product.
Another way of preparing the reducing gases is also known, involving the partial combustion of fuel oil and other higher hydrocarbons.
The injection of a sub-stoichiometric mixture of hydrocarbons and air directly into the reducing bed has also been proposed. Although this does away with the costly plants previously needed to make reducing gases, it has its drawbacks: for instance, the sulphur content of the fuel oil, which contaminates the metal produced, the fact that part of the hydrocarbon cracks producing carbon black directly in the reducing bed, and the fact that the nitrogen contained in the air used builds up in the plant.
Accordingly, there is a need for a process eliminating these drawbacks, permitting direct reduction of ores in fluid beds cheaply and with no possibility of the metal produced being contaminated with sulphur.
The FIOR process was developed by ESSO Research and Engineering Company in the late 1950's and early 1960's. The process was intended to produce Direct Reduced Iron (DRI) briquettes by a Fluidized Iron Ore Reduction (FIOR) processing scheme which used iron ore fines as a feedstock. The fluidizing gas was provided by the reforming of light hydrocarbon gases.
The first process development work was done at a 5 ton/day pilot plant at the ESSO Research Labs in Baton Rouge, La. Test work began in 1962 and terminated in 1966. Based upon the preliminary results of this test work, a semi-commerical plant was built in Darmouth, Nova Scotia. The plant had a design capacity of 300 tons/day, and operated from 1965 to 1969. A total of 56,000 tons of DRI briquettes were produced, equivalent to only 15% of the expected production at the design rate.
During the ensuing years, the plant operations personnel continued to improve the process by way of mechanical and operational refinements. These refinements were often implemented in the field without benefit of engineering studies, due to the limited resources of the company. These improvements resulted in a steady increase in production, and the plant reached 96% of design production in 1986.
Competing pellet based DRI processes cannot utilize iron ore fines for feed as the FIOR process does. These processes had previously required much less energy per ton of product, but their energy consumptions have increased recently as they have incorporated hot briquetting, a process that FIOR research pioneered. Therefore, an improved FIOR design could be more viable than competing DRI processes for many areas which possess large quantities of ore fines, have low energy costs, and need to export DRI.
The net result of this developmental process is that the present plant design and operation has improved over the original contemplated designs. A new plant utilizing the FIOR process would have to incorporate the changes in order to be thermally efficient and economical. In addition to these already implemented changes, a new plant design would have to include equipment and process improvements that are made possible by current technology and by better knowledge of the process shortcomings.
The previous design was not intended to be thermally efficient due to the very low natural gas prices that were prevalent 15 years ago. Today, a DRI plant has to be as thermally efficient as possible due to the high incidence of fuel cost upon the overall production cost, even in countries with relatively inexpensive energy. The improved design contemplates a 25% decrease in energy requirements as compared to the previous design.
The plot configuration utilized in the previous design was not optimized with respect to economy of layout. The previous design is a hybrid of old refinery and steelmaking technology, and is characterized by large plot areas. Competing DRI processes are much more compact. A more compact FIOR plant layout would result in economies of construction (less piping and structure) and operation (fewer operators). The improved design will result in a reduction in plant operating equipment plot areas of up to 40%, and a decrease in operating manpower of up to 25%.
Another area covered by the improved design is mechanical reliability. Some pieces of mechanical equipment that have historically been troublesome in the previous design are either replaced by more reliable equipment or removed in the improved design. In addition, design improvements have been included to eliminate problems of dust ingestion into equipment, which has caused equipment operating problems in the previous design.